Dendritic spines are specialized actin-rich protrusions that serve as primary recipients of most excitatory synapses in the brain. Spines are extremely dynamic, exhibiting diverse structural and functional changes during development, in response to stimuli, as well as in learning and memory. While there is substantial evidence that several neurodevelopmental and psychiatric diseases converge on a common theme of aberrant spine formation, the mechanisms of spine formation and how its dysfunction relates to disease is unclear. TAOK2 is a serine/threonine kinase implicated in neuronal development, and is one of the genes present in the 16p11.2 genomic locus. Deletion of this region is the most common risk factor associated with autism spectrum disorder (ASD). Despite its relevance in neuronal development and to ASD, the physiological neuronal substrates of TAOK2 kinase are not known. It is unclear how TAOK2 signaling mediates spine development and how an imbalance in TAOK2 gene dosage might contribute to neuronal and behavioral alterations associated with ASD. Using a combination of innovative approaches, this proposal aims to delineate the mechanistic role of TAOK2 kinase during synaptogenesis and to understand how dysfunction in this signaling pathway might contribute to disease. As a postdoctoral fellow in Dr. Yuh-Nung Jan's laboratory at UCSF, I have gained skills in neurobiology, mass spectrometry, and chemical-genetics in addition to my graduate background in cell biology and biochemistry. For the experiments proposed in this application, I seek interdisciplinary mentored training in stem cell technology, super-resolution microscopy, and quantitative proteomics. I have assembled a team of mentors with expertise in: mass spectrometry and proteome-scale data acquisition and analysis (Dr. Al Burlingame), iPSC technology (Drs. Kathryn Ivey and Lauren Weiss), neurodevelopment and ASD (Dr. John Rubenstein), and super-resolution microscopy (Dr. Bo Huang). This training will allow me to achieve the following aims: 1) systematic investigation of TAOK2 localization during spine development using super-resolution STORM imaging, 2) identification and characterization of direct novel targets of TAOK2 kinase using a chemical-genetic approach, and 3) characterization of the TAOK2 pathway in ASD pathology using iPSC derived neurons from 16p11.2 deletion patients. With the new training and information acquired in the K99 phase, I will extend the scope of my research in the R00 phase. I will analyze the role of the identified TAOK2 phosphorylation targets during neuronal development. I will also perform phosphoproteomic analysis of 16p11.2 deletion iPSC-derived neurons to identify global changes caused by imbalances in TAOK2 dosage, which may reveal clinically relevant insights into the pathogenesis of ASD. The training period afforded by the K99/R00 award will greatly facilitate my long-term goal as an independent investigator to elucidate signaling pathways involved in dendritic spine formation during normal and disease states.